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AST FINAL > AST FINAL > Flashcards

AST FINAL Flashcards

1
Q

the total # of stars in the observable universe. is….

A

the # of grains on all the earths braches

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2
Q

speed of light in km

A

300,000 km per second

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3
Q

how long does it take light to go from the moon to earth

A

1 second

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4
Q

how long does it take light to travel from the earth to the sun

A

8 minutes

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5
Q

Which of these layers of the Sun is coolest?

A

photosphere

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6
Q

layers of sun from out to in

A

corona, chromosphere, photosphere

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7
Q

At the center of the Sun, fusion converts hydrogen into

A

helium, energy, and neutrinos.

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8
Q

the (blank) is the layer of the sun between its core and convection zone

A

radiation zone

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9
Q

Based on its surface temperature of 5,800 K, what color are most of the photons that leave the Sun’s surface?

A

green

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10
Q

Sunspots are cooler than the surrounding solar surface because

A

strong magnetic fields slow convection and prevent hot plasma from entering the region

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11
Q

What is granulation in the Sun?

A

the bubbling pattern on the photosphere produced by the underlying convection

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12
Q

What observations characterize solar maximum?

A

we see many sunspots

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13
Q

true or false, the corona brightens in x rays during a solar maximum

A

true

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14
Q

heliosphere

A

a bubble of solar wind which separates our planetary system from interstellar space

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15
Q

A main-sequence star twice as massive as the Sun would last __________.

A

half as long as the Sun

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16
Q

What happens to a low-mass star after helium flash?

A

Its luminosity goes down.

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17
Q

which of the following stars is most massive. AGM

A

A

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18
Q

AFK Which of these stars has the coolest surface temperature?

A

K

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19
Q

where on the HR diagram are cool and dim stars

A

bottom right

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20
Q

where on the HR diagram are hot and luminous stars

A

upper left

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21
Q

Compared to a high-luminosity main-sequence star, stars in the upper right of the H-R diagram are __________.

A

cooler and larger in radius

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22
Q

Compared to a low-luminosity main-sequence star, stars in the lower left of the H-R diagram are __________.

A

hotter and smaller in radius

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23
Q

What would happen to a neutron star with an accretion disk orbiting in a direction opposite to the neutron star’s spin?

A

its spin would slow down

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24
Q

A teaspoonful of white dwarf material on Earth would weigh

A

a few tons

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25
Q

what in size is closest to a white dwarf

A

the sun

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26
Q

true or false, Our Sun will probably undergo at least one nova when it becomes a white dwarf about 5 billion years from now

A

false

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27
Q

What kind of pressure supports a white dwarf?

A

electron degeneracy pressure

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28
Q

What is the upper limit to the mass of a white dwarf?

A

1.4 m sun

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29
Q

After a massive-star supernova, what is left behind?

A

either a neutron star or a black hole

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30
Q

What is the upper limit to the mass of a neutron star?

A

between 2 and 3 m sun

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31
Q

A teaspoonful of neutron star material on Earth would weigh

A

more than mt everest

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32
Q

Which of the following is closest in size (radius) to a neutron star?

A

a city

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33
Q

what would happen if a neutron star hit earth

A

earth would create a 1 cm film over it

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34
Q

From a theoretical standpoint, what is a pulsar?

A

a rapidly rotating neutron star

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35
Q

If you were to come back to our Solar System in 6 billion years, what might you expect to find of the sun?

A

a white dwarf

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36
Q

What does the famous formula have to do with special relativity?

A

It is a direct consequence of the theory, and hence a way of testing the theory’s validity.

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37
Q

true or false. Suppose that, as you sit in your classroom, you see two balls fall to the floor and hit at exactly the same time. According to the theory of relativity, other people sitting in the classroom with you will not agree that the balls hit the floor at the same time.

A

false

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38
Q

true or false? Different observers always agree about the order of events that occur at the same place.

A

true

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39
Q

true or false, the general theory of relativity deals with the effects of gravity, but the special theory of relativity does not take gravity into account.

A

true

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40
Q

The equivalence principle tells us that effects of these two things are indistinguishable:

A

gravity and acceleration

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41
Q

You know that you are following the straightest possible path through spacetime if

A

u r weightless

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42
Q

Why do we think that gravitational waves really exist?

A

We have observed orbiting objects that are losing precisely the amount of energy we expect them to be losing to gravitational waves.

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43
Q

Why do we see a gravitational redshift in the spectrum of the Sun?

A

Time runs slower on the Sun than on Earth, making lines in the solar spectrum have lower frequency and hence longer wavelength than normal.

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44
Q

Where are most of the Milky Way’s globular clusters found?

A

in the halo

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45
Q

Which of these forms of radiation passes most easily through the disk of the Milky Way?

A

infrared light

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46
Q

How does the diameter of the disk of Milky Way Galaxy compare to its thickness?

A

The diameter is about 100 times as great as the thickness.

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47
Q

the diameter of the milky way is?

A

100,000 light years

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48
Q

The Sun’s location in the Milky Way Galaxy is _________.

A

in the galactic disk, roughly halfway between the center and the outer edge of the disk

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49
Q

What do we mean by the interstellar medium?

A

the gas and dust that lies in between the stars in the Milky Way galaxy

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50
Q

What are the Magellanic Clouds?

A

two small galaxies that probably orbit the Milky Way Galaxy

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51
Q

How do disk stars orbit the center of the galaxy?

A

They all orbit in roughly the same plane and in the same direction.

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52
Q

What do we mean by the star-gas-star cycle?

A

It describes the orbits of the stars and interstellar medium around the center of the galaxy.

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53
Q

What are cosmic rays?

A

subatomic particles that travel close the speed of light

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54
Q

Which of the following analogies best describes how the structure of the galaxy’s spiral arms is maintained?

A

Like cars slowing in traffic to look at an accident, stars slow as they pass through the spiral arms.

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55
Q

What do we mean by a protogalactic cloud?

A

a cloud of hydrogen and helium that contracts to become a galaxy

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56
Q

Most stars in the Milky Way’s halo are young or old

A

old

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57
Q

What is an ionization nebula?

A

a colorful cloud of gas that glows because it is heated by light from nearby hot stars

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58
Q

In which of these galaxies would you be least likely to find an ionization nebula?

A

a large elliptical galaxy

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59
Q

true or false. Stars are continually forming in the halo of our Galaxy today.

A

false

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60
Q

true or false Spiral galaxies have more gas, dust, and younger stars than elliptical galaxies do.

A

true

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61
Q

A collision between two large spiral galaxies is likely to produce

A

an elliptical galaxy

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62
Q

The luminosity of a quasar is generated in a region the size of

A

the solar system

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63
Q

The primary source of a quasar’s energy is

A

gravitational potential energy.

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64
Q

Suppose a galaxy forms from a protogalactic cloud with a lot of angular momentum. Assuming its type has not changed due to other interactions, we’d expect this galaxy to be ______.

A

a spiral galaxy

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65
Q

Two ways in which the starting conditions in a protogalactic cloud might cause it to become an elliptical (rather than spiral) galaxy are if the cloud begins with either:

A

relatively little angular momentum or relatively high density

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66
Q

If the Andromeda Galaxy collided with the Milky Way, what would most likely happen to Earth?

A

nothing

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67
Q

Why do nearly all astronomers now agree that quasars really are quite far away?

A

We now have images and spectra that show quasars to be embedded at the centers of distant galaxies and within distant galaxy clusters.

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68
Q

Suppose we observe a source of X rays that varies substantially in brightness over a period of a few days. What can we conclude?

A

The X-ray source is no more than a few light-days in diameter.

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69
Q

Central black holes can be very efficient for converting the mass-energy of infalling matter to thermal energy in the accretion disk. Roughly what percentage of the mass-energy can be converted to other forms of energy as matter falls into a black hole?

A

10-40%

70
Q

Why is a dense cloud more likely to produce an elliptical galaxy than a spiral galaxy?

A

The higher gas density forms stars more efficiently, so all the gas is converted into stars before a disk can form.

71
Q

Which of these binary systems is most likely to contain a black hole?

A

an X-ray binary containing an star and another object of equal mass

72
Q

How would a flashing red light appear as it fell into a black hole?

A

Its flashes would shift to the infrared part of the spectrum.

73
Q

Where would be the most likely place to find an ionization nebula?

A

in a spiral arm

74
Q

If you were to take a voyage across the Milky Way, what kind of material would you spend most of your time in?

A

warm, rarefied clouds of atomic hydrogen

75
Q

Approximately how far is the Sun from the center of the galaxy?

A

28,000 lightyears

76
Q

What is the galactic fountain model?

A

the theory that hot, ionized gas blown out of the galactic disk and into the halo by superbubbles cools down and falls back into the disk

77
Q

Which of these colors of light passes most easily through interstellar clouds?

A

yellow

78
Q

Astronomers estimate that new stars form in our galaxy at the rate of about

A

a few (2-3) a year

79
Q

What is interstellar reddening?

A

Interstellar dust absorbs more blue light than red light, making stars appear redder than their true color.

80
Q

What happens within a contracting cloud in which gravity is stronger than pressure and temperature remains constant?

A

It breaks into smaller fragments.

81
Q

Which kind of object is the best standard candle for measuring distances to extremely distant galaxies?

A

a white dwarf supernova

82
Q

When the ultraviolet light from hot stars in very distant galaxies finally reaches us, it arrives at Earth in the form of

A

visible light

83
Q

The flat part of the Milky Way Galaxy’s rotation curve tells us that stars in the outskirts of the galaxy

A

orbit the galactic center just as fast as stars closer to the center.

84
Q

Based on current evidence, which of the following is considered a likely candidate for the majority of the dark matter in galaxies?

A

subatomic particles that we have not yet detected in particle physics experiments

85
Q

What kinds of atomic nuclei formed during the era of nucleosynthesis?

A

hydrogen and helium and trace amounts of lithium, beryllium, and boron

86
Q

Approximately how long did the era of nucleosynthesis last?

A

3 minutes

87
Q

Why does the Big Bang theory predict that the cosmic background radiation should have a perfect thermal radiation spectrum?

A

The background radiation came from the heat of the universe, with a peak corresponding to the temperature of the universe.

88
Q

What are the two key observational facts that led to widespread acceptance of the Big Bang model?

A

the cosmic background radiation and the high helium content of the universe

89
Q

Olbers’ paradox is an apparently simple question, but its resolution suggests that the universe is finite in age. What is the question?

A

Why is the sky dark at night?

90
Q

In the 1960s, Maarten Schmidt determined that quasars were very distant objects by

A

determining their redshifts.

91
Q

true or false. Quasars are powered by the intense production of large numbers of stars that can only be sustained for a relatively short time.

A

false

92
Q

How is the energy that powers radio galaxies, quasars, and other active galactic nuclei produced?

A

by gravity, which converts potential energy of matter falling toward a central black hole into kinetic energy, which is then converted to thermal energy by collisions among the particles of matter

93
Q

If we represent the Milky Way Galaxy as the size of a grapefruit (10-cm diameter), the distance to the Andromeda Galaxy would be about

A

3m

94
Q

galaxy

A

a great island of stars in space

95
Q

light year

A

9.56 trillion km

96
Q

planet

A

a moderetely sized object that orbits a star and shines primarely by reflecting light from that star. it must 1) orbit a star 2)large enough for its own gravity to make it round 3) has cleared most other objects from its orbital path

97
Q

solar system

A

a star and all the things that orbit it

98
Q

if you put all of history into one year, when were the pyramids built

A

11 seconds ago

99
Q

from above what direction does the earth rotate

A

counterclockwise

100
Q

how fast is the earth spinning

A

1,000 km per hour

101
Q

how fast does the earth orbit the sun

A

100,000 km per hour

102
Q

what is the earths axis tilt

A

23 degrees

103
Q

how long does a galactic rotation take

A

230 million years

104
Q

copernicus

A

polish scientist who applied calculatoins to aristarchus’s sun centered theory and knew it was correct. said it worked with weird circles…

105
Q

Tycho Brahe

A

he used naked eye measurements to prove that supernovas were much farther away than the moon. he produced good data. but he thought that the sun orbited the earth while the other planets orbit the sun

106
Q

kepler

A

hired by tycho. he came to the conclusion that orbits are elliptical

107
Q

keplers 1st law

A

the orbit of each planet around the sun is an ellipse. planets are closer at perihelion and further at aphelion

108
Q

keplers 2nd law

A

as a planet moves around its orbit, it sweeps out equal areas in equal time. therefore, planets move a greater distance when it is near perihelion than it does in the same amount near aphelion. faster when closer to the sun

109
Q

perihelion

A

when a planet is closer to the sun

110
Q

aphelion

A

when a planet is further from the sun

111
Q

keplers 3rd law

A
  • more distant planets orbit the sun slower.
  • P^2=a^3. p is the orbital distance and a is the average distance
  • thought magnetism (not gravity) kept planets orbiting the sun
112
Q

hallmarks of science

A

seeks to explain observed phenomenon that rely on solely natural causes 2) science progresses through the creation and testing of models in nature that explain the obersvations as simply as possible 3) a scientific model must make testable predictions about natural phenomenon that will force us to revise or abandon the model if the predictions do not agree with the observations

113
Q

occam’s razor

A

when a scientist chooses a simpler of 2 models that both work

114
Q

theory

A

a model/generalization that stands up to testing again and again. cannot be proven beyond a doubt

115
Q

conservation of momentum

A

the total momentum of interacting objects cannot change as long as no external force is acting on them. momentum is conserved

116
Q

conservation of angular momentum

A

as long as there is no external torque (twisting force) the total momentum of a set of interacting objects cannot be changed

117
Q

kinetic energy

A

energy of motion

118
Q

radiative energy

A

energy carried by light

119
Q

potential energy

A

stored energy, might be used as kinetic or radiative energy

120
Q

thermal energy

A

the collective kinetic energy of many particles

121
Q

mass energy

A

energy stored in mass

122
Q

newton’s law of gravity

A

1) every mass attracts every other mass through gravity
2) the strength of the gravitational force attracting any 2 objects is directly proportional to the products of their masses
3) the strength of gravity between 2 objects decreases with the square of the distance between their centes (inverse square law)

123
Q

doubling the distance between 2 objects weakens the gravitational force by

A

2^2=4

124
Q

orbiting energy

A

the sum of an orbiting objects kinetic and gravitational energy. this total energy does not change even though one or the other can. balance is kept

125
Q

earths escape velocity

A

40,000 km/hr 11 km/s

126
Q

power

A

the rate of energy flow measured in watts

127
Q

wavelength

A

the distance from one peak to the next

128
Q

frequency

A

the number of peaks that pass through a point in a second

129
Q

photons

A

the particles of light

130
Q

is light a particle or a wave

A

both

131
Q

atomic number

A

the number of protons

132
Q

atomic mass number

A

the number of protons plus neutrons

133
Q

isotope

A

an atom with a different number of protons

134
Q

the only thing that affects a spectrum is

A

temperature

135
Q

hot object= what frequency and wavelength

A

high frequency, short wavelength

136
Q

doppler effect

A

when the spectra of light relative to us changes due to its motion

137
Q

blue shift

A

coming toward us. wavelength shorter

138
Q

redshift

A

moving away from us. wavelength gets longer

139
Q

gravitational contradiction

A

the false theory from the 1800s that says the sun generates energy by slowly shrinking

140
Q

corona

A

outermost level of the sun’s atmosphere that extends several million km above the sun. million k temp. X rays

141
Q

chromosphere

A

middle layer of the suns atmosphere. and the region that radiates the suns UV temp of 10,000

142
Q

photosphere

A

te lowest layer of the suns atmosphere. consists of a gas far less dense than the earths with a temperature of 6,000 k. visible light

143
Q

convection zone

A

. just below atmosphere. where energy generated in the core travels upward, transportated by the rising of hot and cool gas

144
Q

radiation zone

A

where energy moves outward primarily in the form of photons of light. Temp of 10 million k. is right outside the core. lots of x rays

145
Q

core

A

temp of 15 k. fusion happens here

146
Q

proton-proton chain

A

fusion process in low mass stars. 4 h–> 1 he + neutrino

147
Q

what is happening to the brightness of the sun over time

A

generally increasing

148
Q

what causes sunspots

A

magnetic fields poking out

149
Q

solar flares

A

a storm that sends out charged particles of x rays and fast moving particles out into space.

150
Q

sunspot cycle

A

a cycle in which the average number of sunspots on the sun gradually increases and falls. 11 years to go back from where it started from. whole cycle really 22 years

151
Q

if the sun were viewed from 10 times the earths distance, it would be dimmer by a factor of what

A

10^10=100 if it were twice the distance it would be 2^2=4

152
Q

which spectral type is the hottest and bluest OBAFGKM

A

O

153
Q

which is hotter G1 or G9

A

G1

154
Q

visual binary

A

a pair of stars that we can view orbiting eachother

155
Q

eclipsing binary

A

a pair of stars that orbit in the plane of our sight. when neither star is eclipsed, we can see noth stars. when one is eclipsing the other, the brightness of the system drops

156
Q

spectroscopic binary

A

a binary that is neither visual or eclipsing another one, we may detect it through doppler shifts or through spectral lines

157
Q

power

A

the amount of energy emitted per second

158
Q

true or false, The energy levels for electrons vary from one element to another.

A

true

159
Q

What is the meaning of the wordcosmos

A

the sum total of all matter and energy, that is, everything within and between all galaxies

160
Q

a light year is how many km

A

9.46 trillion

161
Q

true or false, A star with spectral type F2 is hotter than a star with spectral type F3.

A

true

162
Q

On a Hertzsprung-Russell diagram, where would we find stars that are cool and luminous?

A

upper righ

163
Q

which side of the HR diagram is cooler

A

the right side

164
Q

agol paradox

A

binary system when the less massive star gets mass from the larger one

165
Q

what keeps a white dwarf from collapsing

A

electron degeneracy pressure

166
Q

what happens to a red watch as it falls into a black hole

A

Eventually It becomes infrared than radio. The clock stops.

167
Q

gamma ray bursts

A

• Some might come from powerful supernova explosions (the kind that creates black holes)

168
Q

what are the 2 ways that stars return gas to the universe through galactic recycling

A

stellar winds or supernova. this process returns gas but also changes the % of heavy elements

169
Q

disk population

A

contains both young and old stars, all of which have heavy element proportions of about 2%, like our sun

170
Q

spheroidal population

A

consists of stars in the halo and the bulge, both of which are roughly spherical in shape. Stars in this population are always old and therefore low in mass, and those in the halo sometimes have heavy element proportions as low as .02%

171
Q

what is the minimum mass of a star and why does it exist

A

.08 and because their central temperatures never climb above 10 million k needed for fussion • Degeneracy pressure, which depends on the mass of an object, halts gravitational contraction before hydrogen burning can begin

172
Q

brown dwarf

A

• The result of a protostar with a mass of .08 and degeneracy pressure is a failed star, that slowly radiates away its thermal energy

AST FINAL (2 decks)

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